However, while the Equalities Office stressed that the scheme was voluntary, Harman told Personnel Today other laws could allow the government to force employers to measure their pay gaps.

“We’re asking people to post their pay gap voluntarily, but we have got a backstop in the Companies Act, which means we can make people do it,” she said.

An Equalities Office spokeswoman stressed that such powers would only be used years down the line if a company repeatedly failed to make improvements in diversity.

Other steps aimed at eradicating inequality should be looked at first, the spokeswoman said, including the use of public procurement, and the introduction of a kite-mark for exemplar organisations.

The Equalities and Human Rights Commission will also investigate sectors which show “clear inequality”. The financial services sector is in the spotlight as it has a gender pay gap of 41.5%, compared with the national average of 12.6%.